1. Field of the Invention:
The present invention relates to a line jointing structure suitable for use in an electrostatic spray coating apparatus, for connecting to a device, an insulating line serving as a path for conveying electrically conductive paint to which a high voltage is applied.
2. Description of the Related Art:
As a method of applying a high voltage to electrically conductive paint so as to electrostatically spray-coat an object or workpiece such as a vehicle body to be coated, with the conductive paint, there has heretofore been known a voltage blocking method, for example. This method has been disclosed in Japanese Patent Application Laid-Open No. 2-2885, for example. According to the disclosure, electrically conductive paint is first introduced into an intermediate reservoir from a paint feed source through an insulating line. Thereafter, the insulating line is washed and dried to create an electrically insulated state (voltage block), thereby preventing current from leaking to the paint feed source. Under this condition, the conductive paint to which the high voltage has directly been applied is supplied to an applicator from the intermediate reservoir, thereby electrostatically spray-coating an object or work with the conductive paint.
In this case, there is often a situation in which the applicator is normally mounted on a reciprocator, a robot, etc. Therefore, a flexible line is used as a path or passage for the transportation of paint. FIG. 1 shows a line connecting or jointing structure for joining the flexible line to another member. In the drawing, numeral 2 indicates a jointing member. One end of the jointing member 2 is coupled to a device 4 such as an applicator, etc., whereas the other end thereof is coupled to a line 10 by a sleeve 6 and a nut 8.
In the aforementioned line jointing structure, however, current tends to leak from a junction between said one end of the jointing member 2 and the device 4, from between the other end of the jointing member 2 and the nut 8 and from between the nut 8 and the sleeve 6. Accordingly, the jointing structure cannot maintain a desired high voltage as it is, thereby causing the problem that the efficiency of an electrostatic spray-coating process is reduced. When dust such as paint adheres to the range from the jointing member 2 to the joined portion and they communicate with each other, current assuredly leaks out. Consequently, it is feared that an electrostatic spray-coating process cannot reliably be carried out. When an electric conductor such as a robot arm approaches the jointing member 2, sparks are produced.
Further, in the above electrostatically spray-coating method of an internal voltage-application type, the range between the applicator and the intermediate reservoir is subjected to a high voltage through the paint over its entirety. Therefore, current leakage tends to occur. In particular, a line jointer for connecting a flexible line which forms a paint feed path to each of various devices develops great possibility of current leakage. There is also often a situation in which a flexible line exerts a counteracting force upon a line jointer for connecting the flexible line to an applicator or upon a line jointer for connecting the flexible line to an intermediate reservoir when the applicator is mounted on a robot or the like to move along a portion of an object or work to be coated with paint or to move reciprocatively. Thus, when an electrostatic spray-coating process is repeated, load acts on each line jointer, so that the flexible line and each line jointer are loosed or free from a state of their connection, thereby causing current leakage. As a result, a high voltage applied to electrically conductive paint changes from a desired value to another so as to make a state of an object or workpiece being electrostatically spray-coated with the paint unstable, thereby causing the problem that the object or workpiece which has been spray-coated with the paint is made inferior in quality.
In order to prevent the flexible line and each line jointer from working loose, there is therefore proposed a method of improving the strength of each line jointer. However, each line jointer must be enlarged in structure, thereby causing the problem that the electrostatic spray-coating or painting apparatus becomes large in size as a whole.